Reduced pyridine compounds

ABSTRACT

Reduced pyridine compounds, including 1,4-dihydropyridine compounds and 1,2-dihydropyridine compounds, are useful as latent image amplifiers. They can be incorporated in a silver halide emulsion or incorporated in a layer adjacent to a silver halide emulsion layer in a photographic element. The reduced pyridine compound may be used in a silver halide developer solution or in an activator solution for use in a silver halide photographic element containing an incorporated developer. Silver halide emulsions when developed in the presence of the reduced pyridine compounds are found to have increased effective speed.

Jnited States Patent lunshi et al.

REDUCED PYRIDINE COMPOUNDS Inventors: Jal F. Munshi; Richard L. White,

both of Rochester, NY.

Appl. No.: 400,276

52] US. Cl 96/66.3; 96/50 R; 96/66 R; 96/76 R; 96/95 31] Int. Cl. G03c5/30; G03c 1/48 i8] Field of Search 96/50, 66 R, 66.3, 76 R, 96/95 i6]References Cited UNITED STATES PATENTS 288,226 6/1942 Carroll et a1..96/107 288,586 6/1942 Dersch et a1 96/665 648,604 8/1963 Welliver eta1 96/663 340,851 6/1960 Beavers et a1 ..96/66.3 520,689 7/1970 Nagne eta1 ..96/66.3 39,048 10/1974 Pool ..96/5O R July 8, 1975 FOREIGN PATENTSOR APPLICATION Primary ExaminerMary F. Kelley Attorney, Agent, orFirm-H. E. Byers [57} ABSTRACT Reduced pyridine compounds, including1,4- dihydropyridine compounds and 1,2-dihyclropyridine compounds, areuseful as latent image amplifiers. They can be incorporated in a silverhalide emulsion or incorporated in a layer adjacent to a silver halideemulsion layer in a photographic element. The re duced pyridine compoundmay be used in a silver halide developer solution or in an activatorsolution for use in a silver halide photographic element containing anincorporated developer. Silver halide emulsions when developed in thepresence of the reduced pyridine compounds are found to have increasedeffective speed.

24 Claims, No Drawings 1 REDUCED PYRIDINE COMPOUNDS BACKGROUND OF THEINVENTION This invention concerns silver halide emulsions containingreduced pyridine compounds as latent image amplifiers and photographicelements containing a reduced pyridine compound in at least one layeradjacent to a silver halide layer. It also concerns silver halidedeveloper solutions and activator solutions containing reduced pyridinecompounds as latent image amplifiers and silver halide photographicelements containing the reduced pyridine compounds. The invention alsoconcerns the process of using the reduced pyridine compounds as latentimage amplifiers by developing a silver halide emulsion in the presenceof the reduced pyridine compounds.

In the development of photographic materials, it is often desired toincrease effective photographic speed of the photographic materials. Toobtain this, however, many compounds known in the art as developmentaccelerators increase not only effective emulsion speed but also changethe contrast of the developed emulsion. Changes in contrast may not bedesirable for normal photographic purposes. For example, increasedcontrast affects the appearance of the picture to the extent that thepleasing middle tones and details in the shadow and highlight areas arefrequently lost. Moreover, many of the known development acceleratorsincrease the fog appreciably of the silver halide emulsion, a featurewhich is always undesirable. In addition, some of the known developmentaccelerators are not compatible with silver halide emulsions and canonly be incorporated in a developing solution or activator solution.

US. Pat, No. 2,648,604, issued Aug. 11, 1953 to Welliver et al.,discloses a photographic developer containing a pyridinium salt andprocess of development. However, when a compound of the type disclosedin this patent is added to a silver halide emulsion, as illustrated inExample 6, below, it is found to have little effect on the relativespeed of the emulsion.

US. Pat. No. 3,062,645, issued Nov. 6, 1962 to Carroll, also describesdevelopment accelerators but when used in an emulsion as described inExample 7, below, did not appear to effectively increase the relativespeed as compared to the compounds of the invention.

Accordingly, it has been desirable to obtain com pounds (latent imageamplifiers) which can be used either in a developer solution or in asilver halide element which will increase the effective speed withouthaving a significant increase in fog or contrast and when used in aphotographic element also act as chemical sensitizers.

SUMMARY OF THE INVENTION A developer or activator solution is preparedhaving a reduced pyridine compound as a latent image amplifier. Latentimage amplifier" is a term used to define a compound which, in additionto acting as a development accelerator, also acts as a chemicalsensitizer when incorporated in a photographic element. The amplifiercan be added to the black-and-white developer or to an alkalinecolor-forming developer in which a primary aromatic amine is used as adeveloping agent. In a preferred embodiment, reduced pyridine compoundsare added to a developer solution containing hydroquinone andN-methyl-p-aminophenol sulfate having a pH of about 1 l. In anotherembodiment, the reduced pyridine compounds are added to a silver halideemulsion or to a layer adjacent to a silver halide emulsion.

DETAILED DESCRIPTION OF THE INVENTION A wide range of described reducedpyridine compounds can be employed according to the invention. Suitablel,4-dihydropyridine compounds include, for example, compounds of theformula:

in which R is carbamoyl, carboxyalkyl, alkoxycarbonyl, acyl, all havingl-S carbon atoms, cyano or halogen; R' is aryl, aralkyl or alkyl,substituted or unsubstituted, having l-12 carbon atoms; R is hydrogen orhalogen: and 1,2-dihydropyridine compounds having the formula in whichR' and R"" are each selected from the class consisting of an aliphaticradical of not more than five carbon atoms, said radical selected fromthe group consisting of alkyl, chloroalkyl, bromoalkyl, hydroxyalkyl.carboxymethyl, carbalkoxymethyl and alkoxyalkyl, and R' and R"", whentaken together are atoms forming a 5-6 member heterocyclic ringcontaining an O. N, or S atom. Particularly useful compounds aredisclosed in the following Compound Identification Table. When used in adeveloper solution, the concentration is typically within the range ofabout 0.020 to about 0.300 grams per liter, preferably 0.025 to 0.150grams per liter. When used in a silver halide emulsion, theconcentration is about 2.0 to about 300.0 milligrams per mole of silver,preferably about 6.0 to about 100.0 milligrams per mole of silver. Thisis also the concentration typically used when the latent image amplifieris incorporated in a layer adjacent to the silver halide emulsion layer.

Compound R R R" Name I -CONH CH H l-Benzyll ,4-dihydronicotanamide ll-COOCH; -CH H Methyl-l-benzyI-l ,4-dihvdronicotinate lll -COCH;, -CH H3-Acetyll -benzyll ,4-dihydropyritline lb CONH -CH;, H S-Carhumoyl-,4-dihydro l -methyI-pyridine VI CN -CH;, H 3-Cyano-l ,4-dihydrol-methylpyridine VI --COCH; -CH-,CH; H 3-Acelyll ,4-dihydro- 1-ethylpyridine V": CI -CH-,C,,H;, Cl l-Benzyl-3.5-dichloro-l.4dihydro-pyridine IX ErON -CH-,C,,H H l-Benzyl-3-bromol,4-dihydropyridine H H 2(3-Carbamoyl-l.4-dihydro-1-pyridyll-hydroquinone 1,2-Dihydropyridine Compounds X8-Chloro-3-methyl-l-phenyll H-pyrido-l 2,1-h lbenzothiazole Photographicsilver halide emulsions, preparations, addenda, processing and systemsare disclosed in Product Licensing Index, Volume 92, December 197],Publication 9232, pages 107-110, Paragraphs l-XXV.

The reduced pyridine compounds of the invention can be added todeveloper solutions, including those referred to in the ProductLicensing lndex referred to above, a. any time during the preparation ofthe developing solution.

In addition. the reduced pyridine compounds may be used in activatorsolutions at the same concentrations as used in a developer solutionwhen the developer is incorporated in the photographic element.

Alkaline activators which can be employed in developing a latent imagein a photographic element as described include any of those whichprovide the desired activation of the described silver halide developingagent precursor. These include, for instance, aqueous alkaline activatorsolutions commonly employed in rapid access processing of photographicelements, such as those employed in so-called reader-printers. Alkalineactivators which are suitable include inorganic alkali such as alkalimetal hydroxides, especially sodium hydroxide, potassium hydroxideand/or lithium hydroxide, alkali metal carbonates, such as sodiumcarbonate and potassium carbonate, sodium or potassium phosphates, andorganic alkaline development activators such as quaternary ammoniumbases and salts and alkanolamines such as ethanol amine, and similaralkaline materials and/or alkali releasing materials. Such developmentactivators can be applied to the photographic element employed in thepractice of the invention in any suitable manner, including for example,dipping, spraying and/or surface application such as with rollers, asdescribed in U.S. Pat. No. 3,025,779 of Russell et al issued Mar. 20,1962 or by surface application processing as described in U.S. Pat. No.3,418,132 of Kitze issued Dec. 24, 1968.

If desired an alkaline solution can be employed containing conventionalsilver halide developing agents, such as those described. So-called webprocessing can be employed as described, for example, in U.S. Pat. No.3,179,517 ofTregillus et a1. issued Apr. 20, 1965 or socalledstabilization processing as describes in Russell et al., PSA Journal,vol. 161), Aug, 1950.

The time for processing a photographic element in the practice of theinvention, that is developing and sta bilizing a desired latent image,can vary over a wide range, typically between about 1 second to severalminutes depending on the desired image, processing conditions and thelike.

The conditions for processing can also vary. but usually ambientpressures and temperatures of about 20C. to about 30C. are employed.lfdesired, higher temperatures can be used such as temperatures up toabout 50C.

It can be useful in some cases to wash the resulting photographicelement after processing with water, such as a water rinse, for about 1second to about 5 seconds to remove water-soluble compounds. This canimprove post-processing stability and reduce any strain.

The photographic silver halide developer solutions can comprise a silverhalide solvent. Typical silver halide solvents include, for example,alkali metal or ammonium thiosulfates and thiocyanates, such as sodiumthiosulfatc, sodium thiocyanate or ammonium thiocyanulc.

The developer solution, as described, can be a monobath. Typicalcompounds of monobaths are described, for example, in the MonobathManual," by Grant M. Haist, published by London Press, 1966.

The following examples are included for a further understanding of theinvention:

EXAMPLE l A developing solution having the following formulation isprepared.

Formula Hydroquinone 40.0 grams Sodium sulfite 60.0 grams Elon(N-methyl-p-aminophenol sulfate) 10.0 grams Potassium bromide 5.0 gramsDistilled water to 1.0 liter Potassium hydroxide to pH 1 1.2

To portions of this developing solution are added the latent imageamplifiers (reduced pyridine compounds) of the present invention at theconcentrations indicated below. Samples of a coarse grain, medium speed,silver bromoiodide gelatin emulsion (Type A) are exposed (1/50" Neg.)**and the samples are then processed in a roller transport processor (28sec. development at 32C) with the following photographic results. 500watt exposure on an Eastman Model 18 Sensitometer at a color temperaturedistribution of 2650 to 5400 Kelvin. Trademark Samples of a fine grainsilver bromoiodine gelatin emulsion (Type B) are exposed and processedas in Example l, except a 14 sec. development time is used.

Relative Compound g/l. Speed Contrast Fog Control 1.79 .06 l .025 1591.50 .08 l .050 263 1.33 .16

EXA MPLE 3 The photographic elements of Examples 1 and 2 are processedfor 56 sec. and 40 sec. respectively, in a developer as described inExample 1 plus 0.06 g/l. S-methyl-benzotriazole plus 0.25 g/l.S-nitroindazole containing a compound of the present invention.

Relative Emulsion C om g/ l. Speed Contrast Fog pound Type A Control 1002.23 .08 Type A l .10 I35 2.42 .08 Type A l .20 148 2.99 .08 Type A 1.30 200 3.65 .03 Type B Control I 2.03 .06 Type B 1 .10 ns 2.16 .06 TypeB l .20 126 2.43 .06 Type B I .30 166 2.50 .06

EXAMPLE 4 A monodispersed fine grain silver bromoiodide emulsion (TypeB) is given a finishing treatment with sodium thiosulfate. potassiumchloroaurate and sodium thiocyanate. The reduced pyridine compounds areadded to this emulsion. coated on a support, exposed (1/5" Pos)* andprocessed in Kodack Developer D-l9 a high contrast developer having theformula pmethylaminophenol sulfate 8.8 g.; sodium sulfite. dessicated,384.0 g.; hydroquinone 35.2 g.; sodium carbonate. dessicated, 192.0 g.;potassium bromide 20.0 g.; cold water to make 4.0 liters. The resultsare shown below:

"500 watt exposure on an Eastman Model lB Sensitometer at a colortemperature of 3000"Kelvin.

Concentration Relative Compound (mg/mole of Ag) Speed Contrast FogControl 100 2. l .04 I 5 209 l .7 .06 X 2 5 l 3 2 .0 .04 X 6 603 l .9.24

Quaternary pyridinium compounds which speed up the early part of adevelopment process are commonly referred to as developmentaccelerators. The oxidized form of l which isl-benzyl-3-carbamoylpyridinium chloride (Xl) is inactive in thedeveloper solutions under the test conditions outlined above. Furthertests with this compound incorporated in silver halide emulsions clearlyexclude it as the active component.

EXAMPLE 5 Solutions of compounds I, XI and 2-methyl-lphenethylpyridinium iodide (Xll) are added to an emulsion of Type B and digestedfor 10 minutes at 40C. These are coated on a support, exposed (l" Pos)*and processed in an Elon-hydroquinone developerv 500 watt exposure on anEastman Model H; Sensitometer at a color temperature of 3000 Kelvin.

EXAMPLE 6 Tetradecamethylenebis( l l -pyridinium )perchlorate (Xlll) isdescribed in US. Pat. No. 3,062,645 as a de velopment accelerator. lt iscomparatively tested in emulsion of Type B, exposed (1/5" Pos)* andprocessed in Kodak Developer Dl9, as shown below:

Concentration Relative Compound (mg/mole of Ag) Speed Contrast FogControl 3.0 .04

This illustrates the improved results obtained by the compounds of theinvention.

EXAMPLE 7 A medium speed bromoiodide emulsion (Type C) is given afinishing treatment with sodium thiosulfate, potassium aurochlorate andsodium thiocyanate. Compound X is added to it, digested for 5 minutesand coated, exposed (1/50" Neg) and processed in Kodak Developer D-l9 (3minutes).

500 watt exposure on an Eastman Model lB Sensitometer at a colortemperature of 3000" Kelvin.

Concentration Relative Compound (mg/mole of Ag) Speed Contrast FogControl 100 1.8 .18 X 0.5 182 1.9 .36

EXAMPLE 8 Reduced pyridines are also incorporated in a gelatin overcoatspread over the emulsion layer. A conventional antifoggant is added toemulsion of Type C and coated, Compound I is added to a gelatin solutionwhich is spread at a uniform concentration over the emulsion layer,exposed (1/50" Neg)" and processed in Kodak Developer D-l9.

"500 watt exposure on an Eastman Model [B Sensitometer at a colortemperature distribution of 2650 to 5400 Kelvin.

Concentration Relative Com pound (mg/m"') Speed Contrast Fog Control I002.00 .08 l I08 l5 1 1.94 .13

EX AMPL E 9 Compound I is added to a gelatin solution which is spreaduniformly over a coarse grain, medium speed. silver bromoiodide gelatinemulsion (Type A) at a concentration of 6.5 mg/m exposed (1/50" Neg)**and processed in Kodak Developer Dl9.

"500 watt exposure on an Eastman Model 18 Sensitometer at a colortemperature distribution of 2650 to 5400 Kelvin.

Relative Compound Speed Contrast Fog Control l00 196 .05

l l48 L94 l 0 The invention has been described with particular referenceto preferred embodiments thereof but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

We claim:

1. An alkaline photographic developer composition for silver halidecomprising an aromatic silver halide developing agent and a reducedpyridine compound selected from the class consisting ofl,4-dihydropyridine compounds having the formula:

I RYI'I wherein R' and R"", taken separately. are each an aliphaticradical of not more than five carbon atoms that is selected from thegroup consisting of an alkyl radical. a chloroalkyl radical, abromoalkyl radical, a hydroxyalkyl radical, a carboxymethyl radical, acarbalkoxymethyl radical and an alkoxy alkyl radical and R' and R"",taken together, are the atoms necessary to form a -6 member heterocyclicring containing an O, N or S atom.

2. An alkaline photographic developer composition of claim 1 containingl-benzyl-1,4- dihydronicotinamide.

3. An alkaline photographic developer composition of claim 1 containingmethyl-l-benzyl-l ,4- dihydronicotinate.

4. An alkaline photographic developer composition of claim 1 containing3-acetyl-l-benzyl-l ,4- dihydropyridine.

5. An alkaline photographic developer composition of claim 1 containingB-carbamoyl-l,4-dihydro-lmethyl-pyridine.

6. An alkaline photograhie developer composition of claim 1 containing3-cyanol ,4-dihydrol methylpyridine.

7. An alkaline photographic developer composition of claim 1 containing3-acetyl-l,4-dihydro-lethylpyridine.

8. An alkaline photographic developer composition of claim 1 containingl-benzyl-3,5-dichloro-l,4 dihydropyridine.

9. An alkaline photographic developer composition of claim 1 containingl-benzyl-3-bromo-l ,4- dihydropyridine.

10. An alkaline photographic developer composition of claim 1 containing2(3-carbamoyl-l ,4-dihydro-1- pyridyl)-hydroquinone.

11. An alkaline photographic developer composition of claim 1 containing8-chloro-3-methyl-4-phenyl-lH- pyridobenzothiazole.

[2. A process for the development of a photographic image, comprisingtreating an exposed silver halide emulsion with an alkaline photographicdeveloper composition comprising an aromatic silver halide developingagent, said treatment being in the presence of a latent image amplifierwhich is selected from the class consisting of 1,4-dihydropyridinecompounds having the formula:

wherein R is a carbamoyl radical, a carboxyalkyl radical having from 1to 8 carbon atoms, an alkoxycarbonyl radical having from l to 8 carbonatoms, an acyl radical having from 1 to 8 carbon atoms, a cyano radicalor a halogen atom; R is an aryl radical or an alkyl radical, each beingsubstituted or unsubstituted and having from 1 to l2 carbon atoms; andR" is a hydrogen atom or a halogen atom, and l,2-dihydropyridinecompounds having the formula:

wherein R' and R"", taken separately, are each an aliphatic radical ofnot more than five carbon atoms that is selected from the groupconsisting of an alkyl radical, a chloroalkyl radical, a bromoalkylradical, a hydroxyalkyl radical. a carboxymethyl radical, acarbalkoxymethyl radical and an alkoxy alkyl radical and R' and R"".taken together, are the atoms necessary to form a 5-6 memberheterocyclic ring containing an O, N or S atom.

13. A photographic image forming composition comprising silver halideand a reduced pyridine compound selected from the class consisting ofL4- dihydropyridine compounds having the formula:

wherein R is a carbamoyl radical, a carboxyalkyl radical having from 1to 8 carbon atoms, an alkoxycarbonyl radical having from l to 8 carbonatoms, an acyl radical having from 1 to 8 carbon atoms, a cyano radicalor a halogen atom; R is an aryl radical or an alkyl radical, each beingsubstituted or unsubstituted and having from 1 to 12 carbon atoms; andR" is a hydrogen atom or a halogen atom, and l,2-dihydropyridinecompounds having the formula:

p I t, ,r

l ii 't/ i wherein R' and R", taken separately, are each an wherein R isa carbamoyl radical, a carboxyalkyl radical having from l to 8 carbonatoms, an alkoxycarbonyl radical having from I to 8 carbon atoms, anacyl radical having from 1 to 8 carbon atoms, a cyano radical or ahalogen atom, R is an aryl radical or an alkyl radical, each beingsubstituted or unsubstituted and having from 1 to 12 carbon atoms; andR" is a hydrogen atom or a halogen atom, and l,2-dihydropyridinecompounds having the formula:

wherein R' and R"", taken separately, are each an aliphatic radical ofnot more than five carbon atoms that is selected from the groupconsisting of an alkyl radical, a chioroalkyl radical, a bromoalkylradical, a hydroxyalkyl radical, a carboxymethyl radical, acarbalkoxymethyl radical and an alkoxy alkyl radical and R' and R"",taken together, are the atoms necessary to form a 5-6 memberheterocyclic ring containing an O, N or S atom.

15. A photographic element of claim 14 containingl-benzyl-1,4-dihydronicotinamide 16. A photographic element of claim 14containing methyl-l-benzyl-1,4-dihydronicotinate.

17. A photographic element of claim 14 containing S-acetyll -benzyll,4-dihydropyridine.

18. A photographic element of claim 14 containing 3-carbamoyl-l,4-dihydrol-methyl-pyridine.

19. A photographic element of claim 14 containing 3-cyano-l,4'dihydrol-methylpyridine.

20. A photographic element of claim 14 containing S-acetyll ,4-dihydrol-ethylpyridine.

21. A photographic element of claim 14 containing l-benzyl-3,5-dichlorol,4-dihydropyridine,

22. A photographic element of claim 14 containing l-benzyl-3-bromo-l,4-dihydropyridine.

23. A photographic element of claim 14 containing 2(3-carbamoyll,4-dihydrol-pyridyl)-hydroquinone.

24. An alkaline photographic element of claim 14 containingS-chloro-3-methyl-4phenyll H-pyridobenzothiazole.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTIONPATENT N0. 3,893,862

DATED July 8, 1975 INVENTOR(S) Jal F. Munshi and Richard L. White I! iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 7, line 59, photograhid' should read ---photographic--.

Column 8, line 9, should read pyrido-[2,l-b] benzothiazole Column 9,lines 33-42 the formula should read as follows Column 9, lines 10-18 theformula should read as follows H H rr R Column 10, line 5, before theword "hehzothiazole insert [2,1-b]

glgncd and Scaled this [SEAL] thirtieth D3) 0f September1975 Arrest:

RUTH C. MASON ummrssrnrrcr u] Pan-ms and Trademarks

1. AN ALKALINE PHOTOGRAPHIC DEVELOPER COMPOSITION FOR SILVER HALIDECOMPRISING AN AROMATIC SILVER HALIDE DEVELOPING AGENT AND A REDUCEDPYRIDINE COMPOUND SELECTED FROM THE CLASS CONSISTING OF1,4-DIHYDROPYRIDINE COMPOUNDS HAVING THE FORMULA:
 2. An alkalinephotographic developer composition of claim 1 containing1-benzyl-1,4-dihydronicotinamide.
 3. An alkaline photographic developercomposition of claim 1 containing methyl-1-benzyl-1,4-dihydronicotinate.4. An alkaline photographic developer composition of claim 1 containing3-acetyl-1-benzyl-1,4-dihydropyridine.
 5. An alkaline photographicdeveloper composition of claim 1 containing3-carbamoyl-1,4-dihydro-1-methyl-pyridine.
 6. An alkaline photograhicdeveloper composition of claim 1 containing3-cyano-1,4-dihydro-1-methylpyridine.
 7. An alkaline photographicdeveloper composition of claim 1 containing3-acetyl-1,4-dihydro-1-ethylpyridine.
 8. An alkaline photographicdeveloper composition of claim 1 containing1-benzyl-3,5-dichloro-1,4-dihydropyridine.
 9. An alkaline photographicdeveloper composition of claim 1 containing1-benzyl-3-bromo-1,4-dihydropyridine.
 10. An alkaline photographicdeveloper composition of claim 1 containing2(3-carbamoyl-1,4-dihydro-1-pyridyl)-hydroquinone.
 11. An alkalinephotographic developer composition of claim 1 containing8-chloro-3-methyl-4-phenyl-1H-pyrido- benzothiazole.
 12. A process forthe development of a photographic image, comprising treating an exposedsilver halide emulsion with an alkaline photographic developercomposition comprising an aromatic silver halide developing agent, saidtreatment being in the presence of a latent image amplifier which isselected from the class consisting of 1,4-dihydropyridine compoundshaving the formula:
 13. A PHOTOGRAPHIC IMAGE FORMING COMPOSITIONCOMPRISING SILVER HALIDE AND A REDUCED PYRIDINE COMPOUND SELECTED FROMTHE CLASS CONSISTING OF 1,4-DIHYDROPYRIDINE COMPOUNDS HAVING THEFORMULA:
 14. A photographic element comprising a support having thereonat least one silver halide layer and a reduced pyridine compoundselected from the class consisting of 1,4-dihydropyridine compoundshaving the formula:
 15. A photographic element of claim 14 containing1-benzyl-1,4-dihydronicotinamide.
 16. A photographic element of claim 14containing methyl-1-benzyl-1,4-dihydronicotinate.
 17. A photographicelement of claim 14 containing 3-acetyl-1-benzyl-1,4-dihydropyridine.18. A photographic element of claim 14 containing 3-carbamoyl-1,4-dihydro-1-methyl-pyridine.
 19. A photographic element of claim 14containing 3-cyano-1,4-dihydro-1-methylpyridine.
 20. A photographicelement of claim 14 containing 3-acetyl-1,4-dihydro-1-ethylpyridine. 21.A photographic element of claim 14 containing1-benzyl-3,5-dichloro-1,4-dihydropyridine.
 22. A photographic element ofclaim 14 containing 1-benzyl-3-bromo-1,4-dihydropyridine.
 23. Aphotographic element of claim 14 containing2(3-carbamoyl-1,4-dihydro-1-pyridyl)-hydroquinone.
 24. An alkalinephotographic element of claim 14 containing8-chloro-3-methyl-4-phenyl-1H-pyrido- benzothiazole.